When I do my own, I approach it a little more simply. I mark 1/8" down from the top on the side at the neck block. Then with a longish hand plane (#5 or so) I plane around the sides toward the waist to taper, then with a flat sanding batten (a flat dish might do, but I don't use them) to even it up. You now have a flat upper bout. I always use a flat UTBrace. The picture below shows what you are after. You can do 1/2 of this and use a straight edge laid on the now-flat bout with the top temporarily clamped on pointing towards the bridge to verify you are on the right path, then take off the top and do the other 1/2 or whatever you need.

You could do the whole thing with a sanding batten it you were patient, but if you are confident in your planing skills, it just takes a minute to lower it by planing. This has worked fine for me in 3 different sizes - Gibson L-1 with 12-3/4 lower bout, Gibson J-185 with 16" LB, and a small body short scale that I made up with 12-1/2" LB which I used 3/32" instead of 1/8"

That does seem a lot easier to wrap my head around, Ruby. That technique is along the lines of what I was going to do. I’d already done something similar when I radiused the top as well - mostly because using a little block plane is quicker and less messy too. I wasn’t sure how far to measure down but I figure that 1/8” is about how far down the sides are at the apex of the upper bout anyway. The objective is to have a flat surface for the UTB to lay across but I’m shooting for 1.5 degree angle on that neck block tongue too. The way I figure it I’ll start there with the block plane to get that angle set and then focus on the rims from the waist on down.

OK, I have to admit that I couldn't quite wrap my head around how much to plane so I spent several hours sanding before I decided that my back had had enough. I'm otherwise a patient person - though really I think the term "procrastinator" is more apt to my personality!

FWIW I'm much closer to being where the profile needs to be. The holdup now is the A-Frame that locks into the neck block extension. I need to adjust the depth of the mortises in the neck block extension. Once that's done I'm going to do a light test and see if there's any leaks. That will tell me if it's ready for gluing.

I have to admit that I was having trouble understanding why the tail block was the fixed point in this operation until things started to go south. I was worried that I had sanded too much on one side but the waist is still high enough where I see that there’s still a bit of material to come off there. I’d forgotten the point was to establish a flat plat to the bridge, not just to the upper transverse brace.

After two days of sanding, then measuring, then sanding some more - mixed in with routing for bracing every so often I'm getting closer. I was worried that the guitar would not fit in a case meant for a Gibson J-200 (the body on this is deeper) but as I have sanded off 1/8" from the top of the rims I'm not so worried anymore! I was also worried that the mortise for the neck was off because I hadn't accounted for the thickness of the top, but I think that's also being taken care of.

Famous last words, as I like to say though; something is bound to jump up and bite me.

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